International Commission on Radiological Protection (ICRP) has advised about “Protecting people and the environment from the harmful effects of radiation exposure at the appropriate level without unduly limiting the activities involving radiation exposure” in 2007. Application of the ICRP recommendations to medical X-ray exposure in image diagnosis has been recommended.
For the application to medical X-ray exposure, it is necessary to measure the X-ray exposure dose. In PTL 1, information regarding the exposure dose when irradiating a predetermined amount of X-rays for a predetermined period of time is stored in a storing unit, an approximately fixed dose of X-rays reaching each part of the object corresponding to each position in a reconstructed X-ray tomographic image is calculated by an X-ray dose calculation unit, and the exposure dose distribution of the object due to X-rays irradiated when reconstructing the X-ray tomographic image is calculated by an exposure dose distribution calculation unit on the basis of the information regarding the exposure dose, the calculated dose of X-rays reaching each part, and the X-ray irradiation time. Accordingly, the exposure dose distribution for each part of the object is calculated.